The last of the two or three bombs thrown hit Blair on the right shoulder blade, a remarkably accurate throw from 60 feet away. Whilst throwing the bombs (reported to be made from either self-raising or corn flour), one of the organisation members shouted, "Fathers for justice!" Fathers 4 Justice spokesman Matt O'Connor later explained the choice of colour, stating that "purple is the international colour of equality". In the initial aftermath of the incident Blair seemed unperturbed by the incident and looked prepared to continue with the session. SpeakerMichael Martin, however, immediately suspended proceedings and the chamber was rapidly emptied, as fears of a chemical or biological attack mounted.
Many commentators remarked that although the exodus was orderly and without panic, it was in fact the wrong thing to do. If the powder had been a biological or chemical agent, such as sarin or anthrax, then all potentially affected people should have been contained within the affected area in order to prevent any possible further spreading of the toxin.

The incident occurred as Blair was responding to aggressive questioning from Leader of the OppositionMichael Howard. It was reported that in the immediate aftermath of the incident Blair leant across to Howard and said, "I promise you Michael, I didn't organise that!" Howard was reported to respond, "And for once, I believe you!"

Although the incident turned out to be harmless, there were immediate calls for security in the House of Commons to be tightened. Home SecretaryDavid Blunkett, speaking at a Police Federation conference in Brighton, said that such calls were likely to be heeded. Only the previous month a glass security screen had been installed so that members of the public in the Strangers' Gallery specifically could not throw anything into the chamber. The members of Fathers 4 Justice who perpetrated the incident were, however, vouched for by The Baroness Golding, a member of the House of Lords, which allowed them into an unscreened area. Lady Golding had offered the chance to witness the House's operations as a prize in a charity auction, which the group's two members had won.

Upon the resumption of the House at 13:30, the Speaker made a statement and immediately rescinded the right of House of Lords members to allow members of the public into the unscreened area. Golding later made a tearful apology in the House of Lords. The following week, all members of the public were banned from sitting in the unscreened area, even those with an invitation from an MP or peer. Security for the Palace of Westminster is run by the Domestic Committees, rather than the Home Office.

Guy Richard Harrison (48, from Worthing) and Patrick Ronald Davis (36) were arrested and subsequently charged with using threatening, abusive or insulting words or behaviour. The relatively lenient charges, which attract a fine of up to £1000 but no prison sentence, led some in the press to speculate that the harsher charges were not pressed because they would have involved a show trial with Blair and other ministers forced to appear as witnesses, causing more publicity for the group that police are seeking to avoid.